The present invention relates in general to vacuum filters for filtering industrial lubricants and coolants.
More particularly, the invention is concerned with a self-cleaning vacuum filter of the type including a tank for the liquid to be filtered containing a filter assembly, the bottom of which communicates with a vacuum chamber connected to suction means for the liquid, the filter assembly including a screen and an endless loop of regenerable filter cloth having return rollers and movable in steps, by motor-driven entrainment means, over the screen and through a station for the removal of the filtered material, the station extending out of the tank and having means for removing the filtered material from the filter cloth.
Vacuum filters of this type are known, for example, from the present Applicant's European patent application No. 90830303.5.
With these filters, there is a problem in effectively removing the filtered material from the filter cloth so as to prevent it from becoming clogged and to ensure that its filtering characteristics remain constant, as required.
According to the prior art, systems for removing the filtered material from the filter cloth generally include devices for draining or drying the portion of the cloth which emerges from the tank and mechanical or fluid-dynamic removal devices located downstream thereof. For example, in the European patent application cited above, the dried filtered material is removed by a return roller over which the return pass of the filter cloth passes. In other embodiments, nozzles for supplying compressed air are used. In either case, it is not always possible to achieve effective removal and it is necessary to have auxiliary systems, such as devices for washing the belt in a counter-current, or even to replace the belt frequently.